Older adolescence (ages 18-20) is a period of heightened risk taking behavior. In particular, this period has been characterized in part by the propensity towards engagement in risky behaviors (e.g., substance use and abuse, risky sexual behavior, reckless driving) that have the potential for serious physical and psychological consequences. An accumulation of research has demonstrated that peers play a considerable role in older adolescent risk behavior engagement with risk taking often occurring in the peer social context. Although the extant literature has provided insight into the means by which peers may influence risk behavior engagement, studies to date have had a number of limitations. As such, questions remain about how peer influence manifests in the immediate context of risk behavior engagement and which older adolescents are most susceptible/resistant to peer influence. To better understand the proposed influence of peers during risk behavior engagement, the current study aims to understand whether older adolescents act in a riskier manner in the presence of peers and whether peer presence alone influences risk behavior or whether a direct influence process (e.g., peer encouragement of risk behavior) is necessary. Further, the study aims to examine potential moderators of peer influence. Older adolescents are of particular importance in this line of research as they represent an age during which risk behavior is peaking and coupled with the greatest level of autonomy from parents. Using a behavioral risk taking task as the outcome measure, the current experimental study seeks to take an important step towards breaking down the proposed "peer effect." Older adolescents will come to the lab alone once and then be randomized to one of three conditions (alone, peers present, peers encouraging). If the target is randomized to peers present or peers encouraging, the target will be asked to bring in two, same-gender close friends for the second session. In the alone condition, the participant will return without friends. This design allows for the examination of differences in risk taking behavior when peers are a) not present;b) in the same room and able to see participant behavior on the risk task, but unable to provide any form of advice or encouragement in any way;and c) in the same room, able to see participant behavior on the risk task, and given the instruction to encourage risk behavior. In this way, it is possible to isolate peer presence and awareness of behavior from the additional influence of risk encouragement. Results have important implications as they provide a natural extension of previous peer work in a controlled setting providing particular knowledge about the nature of the peer effect, thereby having the potential for improving how the role of peers is conceptualized in prevention and intervention work targeting older adolescent risk taking behavior. PUBLIC HEALTH RELEVANCE: Older adolescence has been characterized in part by the propensity towards engagement in risky behaviors (e.g., substance use and abuse, risky sexual behavior, reckless driving) that have the potential for serious physical and psychological consequences. The goal of the proposed experimental study is to better understand the influence of peers during risk behavior engagement among older adolescents. Results have important implications as they provide a natural extension of previous peer work in a controlled setting providing particular knowledge about the nature of the peer effect, thereby having the potential for improving how the role of peers is conceptualized in prevention and intervention work targeting older adolescent risk taking behavior.